The present invention relates generally to a temperature-adjustable water supply system, and more particularly to a system for supplying water appropriately adjusted in terms of temperature in accordance with intended use, e.g. as bath or shower water.
Japanese Patent Provisional Publication No. 61-112879 discloses an attempt to adjust the temperature of water to be supplied to a water-using object such as shower nozzle, the technique being arranged such that the mixing ratio between hot water and cold water is directly controlled in connection with the opening degrees of a hot-water flow-rate control valve and a cold-water flow-rate control valve which are provided in a hot-water supply passage and a cold-water supply passage, respectively. More specifically, hot water and cold water separately flow through hot-water supply passage and cold-water supply passage, respectively, and mix at a predetermined junction point to further flow through a mixture-water supply passage in a mixed condition. The hot-water supply passage and cold-water supply passage have a hot-water flow-rate control valve and a cold-water flow-rate control valve, respectively, upstream from the predetermined junction point connected to the mixture-water supply passage which is in turn coupled to a water-using object. The temperature of the resulting water mixture is monitored by means of a temperature sensor which is provided in the mixture-water supply passage. A signal indicative of the temperature of the water mixture from the temperature sensor is supplied to a control unit which in turn performs feedback control so that the opening degrees of the hot-water flow-rate valve and cold-water flow-rate valve are respectively adjusted in accordance with the difference between the temperature of the water mixture and a predetermined target temperature. An important problem in such a temperature-adjustable water supply system relates to the difficulty in quickly and stably supplying water at an appropriate temperature. That is, if the break between the water-using periods is relatively long, the temperature of the hot water in the hot-water supply passage is lowered to approximately ambient temperature and therefore the control unit rapidly increases the opening degree of the hot-water flow-rate valve in response to the signal from the temperature sensor of the water-mixture supply passage. This may result in the fact that the temperature of the water mixture to be supplied through the water-mixture supply passage overshooting the predetermined target temperature. Furthermore, in the prior technique, the opening and closing speed of the hot-water and cold-water flow-rate valves is controlled proportionally in accordance with the difference between the water-mixture temperature and the predetermined target temperature. This provides another problem, however, that the temperature of the water mixture easily repeatedly overshoots and undershoots with respect to the predetermined target temperature, resulting in the difficulty being encountered to quickly control the water-mixture temperature so as to be coincident with the target temperature.